The present invention relates generally to spraying finely dispersed liquids contained in a cartridge used in a handheld spraying device, and more particularly to a device and method for locking the cartridge during periods of non-use to avoid leakage therefrom.
Spraying using electrohydrodynamic (EHD) technology (also referred to as electric field effect technology (EFET)) is a process where fluids or other bulk solutions are dispensed through electrically-charged nozzles. In an EHD spray nozzle, the material to be sprayed flows through a region of high electric field strength made possible by the application of a high voltage to the nozzles and associated nozzle geometry. The high voltage causes the fluid material to acquire an electric charge; the electric field present at the nozzle tips applies a pole to the fluid; the poled fluid charge induces a force that acts in opposition to the surface tension of the material. This surface charge causes the formation of at least one ligament of thin jet of material, causing comminution of the fluid into fine droplets.
In one embodiment, EHD spraying devices are incorporated into hand-held sprayers, where additional flexibility can be built in through the use of disposable cartridges. This is beneficial in situations where prolonged or excessive exposure to the fluid being dispensed is undesirable, such as with pesticides or other materials used to treat horses and other domesticated animals. Disposable cartridges typically define a cylindrical fluid storage compartment and include a complementary-shaped piston threadably mounted onto a lead screw, where the piston is driven along the length of the compartment upon rotation of the lead screw. The extension of the lead screw into the compartment causes it to contact the fluid to be dispensed; such a configuration is known as a wetted lead screw. The compartment defines a fluid path with a discharge orifice (or outlet) so that fluid disposed between the piston and the discharge orifice is pumped through the orifice in response to the increasing pressure caused by piston movement toward the orifice.
To reduce the amount of fluid that could leak out between uses, a valve, plug or related flow control mechanism can be placed at or near the discharge orifice to allow the user to shut off the fluid flow. Such an approach works well if the user remembers to open the flow control mechanism before each use; however, if the user should forget to open the flow control mechanism before turning on the pump, pressure will build inside the cartridge that, upon opening the flow control mechanism, would cause the fluid to burst out in an uncontrolled manner, known as a “blurt”.
One method to mitigate blurting would be to use sensors or some other feedback means to prevent the lead screw from being turned when the flow control mechanism is closed. Such remedies are unavailing in cost sensitive cartridge designs. What is desired is a simple, inexpensive way to lock the cartridge. What is further desired is such a way to provide a locking mechanism that can be used on a disposable cartridge.